chore: add metric for missed interruptions events

[ryan-mist]

Fixes #N/A

Description

• adds a new metric when karpenter_interruption_missed_termination_total, that is incremented when a interruptible instance (i.e. spot or from an IODCR) is terminated and Karpenter did not recieve an SQS interruption warning
  • this is done by adding a new annotation, karpenter.k8s.aws/instance-interrupted when Karpenter receives the interruption event

Note that we can't do this through NodeClaim status conditions because Drained as Unknown is the indicating status condition for both case (1) where the SQS interruption warning is not received and (2) when the node was not fully drained before the interruption period is up. We also can't use the InstanceTerminating status condition for the same reason: in cases (1) and (2) it is never set on the NodeClaim. (code ref in core)

How was this change tested?

• unit tests and manual testing

Manual Testing

With correct SQS Qeueue Configured
When an instance is interrupted, the annotation is added:

Annotations:  karpenter.k8s.aws/ec2nodeclass-hash: 13930302764067181154
              karpenter.k8s.aws/ec2nodeclass-hash-version: v4
              karpenter.k8s.aws/instance-interrupted: true

and metric not incremented:

ryanmist@c889f3b6ff52 ~ % curl http://localhost:8080/metrics | grep 'karpenter_interruption'
...
karpenter_interruption_received_messages_total{message_type="capacity_reservation_interrupted"} 2
...
ryanmist@c889f3b6ff52 ~ % curl http://localhost:8080/metrics | grep 'missed_termination_total'
ryanmist@c889f3b6ff52 ~ %

With incorrect SQS QueueConfigured
When an instance is interrupted, the annotation is not added. When its terminated, the metric is incremented:

ryanmist@c889f3b6ff52 ~ % curl http://localhost:8080/metrics | grep 'karpenter_interruption'
# TYPE karpenter_interruption_missed_termination_total counter
karpenter_interruption_missed_termination_total{capacity_type="reserved"} 1
ryanmist@c889f3b6ff52 ~ %

and associated logs:

{"level":"INFO","time":"2026-03-27T01:14:16.926Z","logger":"controller","caller":"cloudprovider/cloudprovider.go:258","message":"detected instance termination without interruption notification","commit":"7d6a7ff-dirty","controller":"nodeclaim.lifecycle","controllerGroup":"karpenter.sh","controllerKind":"NodeClaim","NodeClaim":{"name":"iodcr-pool-dd75k"},"namespace":"","name":"iodcr-pool-dd75k","reconcileID":"2b74ffa4-0036-4865-a43a-158139c7ee5e","provider-id":"aws:///us-west-2c/i-...","Node":{"name":"...","capacity-type":"reserved"}

Does this change impact docs?

• Yes, PR includes docs updates
• Yes, issue opened: #
• No

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

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[AndrewMitchell25]

LGTM 🚀